Posts Tagged ‘Anatomically modern humans’

Many people today seem to like to live in the fear of an impending catastrophe. The fears are all artificial and always include fanciful predictions of doom. Fears of uncontrollable population explosions, food shortages and starvation, of energy crises and depletion of all resources and of course of catastrophic global warming. And they give rise to such utterly useless bodies as the IPCC.

The period from before the last interglacial, the Eemian and through to the current interglacial in the Holocene has seen the rise of Anatomically Modern Humans and, starting from Africa, the peopling of the world. Anatomically modern humans make their appearance in Africa during an even earlier interglacial at around 250,000 years ago. They saw a descent into glacial conditions with global temperatures dropping about 6 °C and sea levels dropping by some 150m. Then around 130,000 to 135,000 years ago a very rapid (relatively) climate change ocurred as the conditions of the Eemian were established. Global temperatures increased by some 7 °C and sea levels rose by upto 170m. Temperatures were warmer than today and sea levels were higher.They didn’t just survive this change – they thrived. They made their way through the Sahara (perhaps through ancient green river corridors) and established themselves in the North and North-East of Africa. At this time sea-levels were high and crossing over into Europe or to Arabia would not have been possible. Both these crossings would have been made at earlier periods by the precursors of AMH and such groups would have given rise to the Neanderthals in Europe and the Denisovans in Asia. When sea levels allowed and perhaps driven by desertfication they crossed into Arabia. From Africarabia they moved across the globe – again perhaps driven by desertification of Arabia.

All these predecessors of ours – some ancestors and some distant cousins – not only survived but actually thrived. They had no IPCC to warn them of looming catastrophe if sea levels rose by 20 cm or temperatures rose by 1.5 °C. Not realising their dangers they still coped with changes of 7 °C and sea-levels of 170 m. Of course they were not without their resources. They had fire. They could probably speak but they had not been contaminated by the written word and were not corrupted by IPCC reports. They may have had some primitive form of rafts but they had no boats and the wheel was unknown. They had stone tools and their version of WMD consisted of many spears. They just coped with the weather and whatever it threw at them. They didn’t waste time predicting the climate and living in the fear of their own predictions. They had other more real fears to worry about.

Former interglacials

The period after the Eemian and upto the present day is particularly interesting. For most of the time the world was in the grip of glacial conditions. Even as the climate changed and the world started warming up, there were sudden spikes of climate in the reverse direction as with the Younger Dryas. It was in this glacial period that AMH left Africa and then peopled the entire globe. It was not a period of stable climate and their expansion and growth took place in an environment of frequent and violent change. Real population increase started some time before the neolithic when we were still hunter-gatherers or semi-nomadic herders.

Age of Human Expansion

Of course in North Africa and the Middle East and Asia where much of the action took place for AMH there was little danger of advancing ice sheets. But there was the constant risk of sudden desertification, the drying up of fresh water resources and the sudden loss or appearance of new coastal land as sea levels increased or decreased. Rainfall patterns would have changed. Landscapes would have been transformed from forests to savannahs to deserts and back again. The only recourse available to humans of that time was to move to a more viable location whenever their survival was threatened.

And as they did that they populated the world and they prospered.

But they could have been stopped in their tracks if they had had the benefit of an IPCC.

Of course this begs the question as to how humans are likely to evolve over the coming generations?

Humans and chimpanzees ancestors split some 7-8 million years ago and it took some 350,000 generations after that divergence for evolution by natural selection to produce anatomically modern humans (AMH). (This of course raises the question as to how chimpanzee evolution proceeded to reach modern chimpanzees while humans were developing into homo sapiens?).

It has been only about 10,000 generations since AMH appeared and only some 6,000 generations or so since modern humans left Africa. A very short time in evolutionary terms yet in this period humans have evolved to exhibit the various races of man that exist today. This differentiation is primarily superficial and all humans existing are capable of mating and producing viable offspring with each other. In theory humans existing today would also be compatible and – in the main – capable of mating with the humans of 6,000 generations ago. In practice a meeting of modern humans with those from 120,000 years ago would be an exaggerated replica of modern man meeting with isolated tribes in the 20th century. These isolated branches of humanity generally had lower levels of immunity to the bacteria carried by their distant cousins and were ravaged by disease after such encounters. The bacteria we carry are probably greatly different to those that humans carried at the dawn of anatomically modern humans. Probably no such meeting or mating would be very successful and one or both would probably succumb to disease brought on by the other’s bacteria. Nevertheless the genomes of the two – even after 6,000 generations – would not be so very different and probably still be compatible. In any primate species a generational distance of over 20,000 between individuals will probably disqualify any theoretical possibility of successful mating.

Their large eyes led to too much of their brain capacity being used for processing visual information and since more of their brain capacity was also needed to handle the motion of their larger, heavier bodies, this resulted in less brain capacity being available for cognitive reasoning. They therefore had “less brain to deal with other functions like social networking”and had“fewer friends to help them out in times of need”. Obviously they then remained culturally trapped in the Stone Age and could not develop written language or Facebook or Agriculture as competing humans eventually did. Apart from a few intrepid and promiscuous Neanderthals who managed to participate in contributing their genes to the human gene pool, all the rest died out.

The only data are measurements of eye sockets in 13 Neanderthal skulls compared to those in 32 human skulls from the same time. All the rest is just conjecture – and then further conjecture based on the original speculation. It would seem to be a little light on data and a little heavy on conjecture. It is still an interesting conjecture nevertheless.

… Looking at data from 27,000–75,000-year-old fossils, mostly from Europe and the Near East, they compared the skulls of 32 anatomically modern humans and 13 Neanderthals to examine brain size and organisation. In a subset of these fossils, they found that Neanderthals had significantly larger eye sockets, and therefore eyes, than modern humans.

The researchers calculated the standard size of fossil brains for body mass and visual processing requirements. Once the differences in body and visual system size are taken into account, the researchers were able to compare how much of the brain was left over for other cognitive functions.

Previous research by the Oxford scientists shows that modern humans living at higher latitudes evolved bigger vision areas in the brain to cope with the low light levels. This latest study builds on that research, suggesting that Neanderthals probably had larger eyes than contemporary humans because they evolved in Europe, whereas contemporary humans had only recently emerged from lower latitude Africa.

‘Since Neanderthals evolved at higher latitudes and also have bigger bodies than modern humans, more of the Neanderthal brain would have been dedicated to vision and body control, leaving less brain to deal with other functions like social networking,’ explains lead author Eiluned Pearce from the Institute of Cognitive and Evolutionary Anthropology at the University of Oxford.

‘Smaller social groups might have made Neanderthals less able to cope with the difficulties of their harsh Eurasian environments because they would have had fewer friends to help them out in times of need. Overall, differences in brain organisation and social cognition may go a long way towards explaining why Neanderthals went extinct whereas modern humans survived.’

‘The large brains of Neanderthals have been a source of debate from the time of the first fossil discoveries of this group, but getting any real idea of the “quality” of their brains has been very problematic,’ says Professor Chris Stringer, Research Leader in Human Origins at the Natural History Museum and co-author on the paper. ‘Hence discussion has centred on their material culture and supposed way of life as indirect signs of the level of complexity of their brains in comparison with ours.

‘Our study provides a more direct approach by estimating how much of their brain was allocated to cognitive functions, including the regulation of social group size; a smaller size for the latter would have had implications for their level of social complexity and their ability to create, conserve and build on innovations.’

Professor Robin Dunbar observes: ‘Having less brain available to manage the social world has profound implications for the Neanderthals’ ability to maintain extended trading networks, and are likely also to have resulted in less well developed material culture – which, between them, may have left them more exposed than modern humans when facing the ecological challenges of the Ice Ages.’

The relationship between absolute brain size and higher cognitive abilities has long been controversial, and this new study could explain why Neanderthal culture appears less developed than that of early modern humans, for example in relation to symbolism, ornamentation and art.

One of the easiest differences to quantify, they found, was the size of the visual cortex—the part of the brain responsible for interpreting visual information. In primates, the volume of this area is roughly proportional to the size of the animal’s eyes, so by measuring the Neanderthals’ eye sockets, they could get a decent approximation of their the visual cortex as well. The Neanderthals, it turns out, had much larger eyes than ancient humans. The researchers speculate that this could be because they evolved exclusively in Europe, which is of higher latitude (and thus has poorer light conditions) than Africa, where H. sapiens evolved.

Along with eyes, Neanderthals had significantly larger bodies than humans, with wider shoulders, thicker bones and a more robust build overall. To account for this difference, the researchers drew upon previous research into the estimated body masses of the skeletons found with these skulls and of other Neanderthals. In primates, the amount of brain capacity devoted to body control is also proportionate to body size, so the scientists were able to calculate roughly how much of the Neanderthals’ brains were assigned to this task.

After correcting for these differences, the research team found that the amount of brain volume left over for other tasks—in other words, the mental capacity not devoted to seeing the world or moving the body—was significantly smaller for Neanderthals than for ancient H. sapiens. Although the average raw brain volumes of the two groups studied were practically identical (1473.84 cubic centimeters for humans versus 1473.46 for Neanderthals), the average “corrected” Neanderthal brain volume was just 1133.98 cubic centimeters, compared to 1332.41 for the humans.

This divergence in mental capacity for higher cognition and social networking, the researcher argue, could have led to the wildly different fates of H. sapiens and Neanderthals. “Having less brain available to manage the social world has profound implications for the Neanderthals’ ability to maintain extended trading networks,” Robin Dunbar, one of the co-authors, said in a press statement. “[They] are likely also to have resulted in less well developed material culture—which, between them, may have left them more exposed than modern humans when facing the ecological challenges of the Ice Ages.”

A new paper in the Journal of Human Evolution claims that the diet of the Neanderthals contained far fewer rabbits than that of Modern Humans. The paper then suggests that this was because Neanderthals could not shift from hunting large prey to hunting small animals. The data may well be valid but the interpretations of the data and the conclusions drawn are so lacking in common sense that the entire paper may well qualify as “idiot science”.

High dependence on the hunting and consumption of large mammals by some hominins may have limited their survival once their preferred quarry became scarce or disappeared. Adaptation to smaller residual prey would have been essential after the many large-bodied species decreased in numbers. We focus on the use of a superabundant species, the rabbit, to demonstrate the importance of this taxon in Iberia as fundamental to predators. We show that the use of the rabbit over time has increased, and that there could have been differential consumption by Neanderthals and Anatomically Modern Humans (AMH). Analysis of bone remains from excavations throughout Iberia show that this lagomorph was a crucial part of the diet of AMH but was relatively unutilised during the Mousterian, when Neanderthals were present. We first present changes in mammalian biomass and mean body mass of mammals over 50,000 years, to illustrate the dramatic loss of large mammalian fauna and to show how the rabbit may have contributed a consistently high proportion of the available game biomass throughout that period. Unlike the Italian Peninsula and other parts of Europe, in Iberia the rabbit has provided a food resource of great importance for predators including hominins. We suggest that hunters that could shift focus to rabbits and other smaller residual fauna, once larger-bodied species decreased in numbers, would have been able to persist. From the evidence presented here, we postulate that Neanderthals may have been less capable of prey-shifting and hence use the high-biomass prey resource provided by the rabbit, to the extent AMH did.

Prehistoric hunters prepare to unleash their throwing sticks at a group of jack rabbits on the run. Painting by Nola Davis, courtesy Texas Parks and Wildlife Department.

That Anatomically Modern Humans ate more rabbits than Neanderthals may well be true but to then leap to the amazing conclusion that Neanderthals were incapable of hunting small prey and then to the even more dubious suggestion that this may have something to do with the demise of Neanderthals as a species takes legitimate speculation into the fantasy worlds of the Land of Painted Caves. We could just as well assume that eating rabbits led to a virulent disease which AMH were immune to but which led to the eradication of the Neanderthal species (except of course for the offspring of those who had mated with AMH) !!

There has been a gap of 50-65,000 years between the genetic time-line of the Out-of-Africa theory and archaeological indications of the earlier presence of anatomically modern humans outside of Africa. But the genetic evidence is now going back in time and approaching the archaeological time-line. “Out-of-Africa” is beginning to look much more like “Out-of-Africarabia”.

Lately, I have been delving into the fascinating – but somewhat arcane – fields of paleo-anthropology and genetics and biology and archeology. I find I am constantly trying to create a narrative which hangs together and looking for the little details which can enable me to personalise and identify with the narrative. It is a search for little “hooks” onto which I can hang my “hats” of understanding. And one such “hook” which both anchors and enables my imagination is that when looked at in the perspective of individuals in a particular line of descent, the ancient past is not as intangible and unreachable as it might seem.

from Wikipedia

It is only simple arithmetic but it seems to me quite remarkable that the long journey from the dawn of anatomically modern humans (AMH) some 250,000 years ago, when considered along any particular line of descent, contains not more than some 12,000 individuals. So the right 12,000 names, if I knew them, would suffice to describe all the individuals on any specific line of descent from my origins as an anatomically modern human. Twelve thousand is not so great a number of people. It is less than the population of the little town I live in and it is a number that would be comfortably handled by even quite a small database. I even hear that some people boast more than 12,000 followers on Twitter and others have more than 12,000 “friends” on Facebook! It does not take many minutes to set up an Excel sheet with 12,000 line items, each line then representing one individual on one of my particular lines of descent.

So I have started a new blogsite called 6,000 Generations to provide an outlet for my speculations about individuals from my Ancestral Generations (AG’s).